Abstract
Relationships among Mg, Ca and P metabolism and parathyroid hormone (PTH) were studied with four ewes which had been fed a control diet for 10 days before experiment. The ewes were fed a low-Mg and low-Ca diet for 10 days (Experiment I), a low-Mg diet supplemented with CaCO3 for 8 days (Exp. II), and a normal-Mg diet supplemented with MgSO4 for 7 days (Exp. III). In Exp. I, the decreased dietary levels of Mg and Ca resulted in a significant fall of the plasma level of PTH. In an old ewe (8 years old) in Exp. II, serum Ca rose strikingly and plasma PTH and serum Mg fell strikingly in level. Hypomagnesemic tetany occurred on the second day and the ewe was not able to stand up, eat or drink on the fourth day. Then plasma PTH rose strikingly in level from the fifth to the seventh days, when the ewe died of tetany. In the other three ewes in Exp. II, the plasma level of PTH did not change during the first half period of Exp. II. It rose to almost the same level as the control during the second half of this experiment, when the ewes lost their appetite. Exp. III was performed with the remaining three ewes. The serum level of Mg fell significantly. The plasma level of PTH also fell. At the same time the urinary excretion of Mg and Ca increased while that of P dropped. The present study suggested that the plasma level of PTH might fall by the deficiency or transient excess of Mg with no relation to Ca intake, and that the great imbalance of dietary Mg and Ca might cause hypomagnesemic tetany by the hypofunction of the parathyriod gland, as was shown in the old ewe.
